1. Field of the Invention
The present invention relates to a drive device for a read and/or write head that uses a micro-actuator, and more particularly, to a magnetic head drive device mounted at a tip of an arm in a drive unit for a magnetic disk or other recording media that eliminates vibration at the arm generated when the micro-actuator is driven, thus permitting precise positioning of the head relative to a desired track on a surface of the magnetic disk.
2. Description of Related Art
In recent years, as the density of recorded information increases, demand has arisen for an actuator arm that can be precisely positioned over extremely short ranges. The demand for precisely positionable dead drive devices is particularly great for head actuators mounted in optical focus correction and tilt control systems, printer devices, magnetic disk drives and the like.
Of these information processing devices, the disk drive units that drive magnetic and other rotating recording media are a key component of the multimedia devices that continue to gain added popularity. Multimedia devices, in order to process more video and audio data at faster speeds, continue to rely on development of higher-capacity equipment. Faster disk drive units, for example, have generally been obtained by increasing the per-disk recording density. However, increasing the recording density without changing the diameter of the disk necessitates increasing the number of tracks per inch, or TPI (as measured along the radius of the disk), that is, the width of the tracks must be narrowed. Additionally, increasing the recording density narrows the track pitch, which in turn requires a head actuator capable of precisely positioning the read/write head (hereinafter referred to as the head) with respect to the recording track.
As a device intended to improve the precision with which the head is positioned, a so-called dual actuator-type head drive device has recently been proposed, which combines a micro-actuator for precise movement of the load arm, slider or head with the conventional head actuator.
For example, the present applicant has previously proposed a micro-actuator for a dual actuator-type assembly employing the shear deflection characteristic of a piezoelectric element. See Japanese Laid-Open Patent Application No. 11-31368. Separately and in addition thereto, a number of piezoelectric and electrostatic head drive devices employing micro-actuators have been proposed.
In general, there are three main types of micro-actuators, depending on the object to be driven, namely head suspension drive, slider drive, and head element.
Here, the slider drive and head element types of micro-actuators require a high degree of precise dimensional machining and have high production costs, both reasons that make the use of the head suspension-drive type of micro-actuator desirable. For these reasons as well, the applicant""s previous submission, Japanese Laid-Open Patent Application No. 11-31368, also had to do with a head suspension type drive mechanism.
It should be noted that the head suspension referenced here comprises a main arm and an elastic sub-arm that is attached to a tip of the main arm, with the head fixedly mounted to the free remaining end of the sub-arm. The head suspension drive type of head movement mechanism disposes a micro-actuator that undergoes a slight displacement between the main arm and the head suspension, so the head (which is at the tip of the head suspension) can be positioned with a high degree of precision.
FIGS. 1A, 1B and FIGS. 2A, 2B are diagrams illustrating a head drive device employing a conventional suspension drive arrangement.
FIGS. 1A, 1B and FIGS. 2A, 2B show an example in which a piezoelectric element is used for the micro-actuator, in particular the shear deflection of the piezoelectric element. The principle of shear deflection is illustrated in FIG. 1A, in which a piezoelectric element 31 is polarized in a direction perpendicular to a direction of a thickness of the piezoelectric element 31 (the direction of polarization indicated by the blank dotted arrow) and electrodes 22A, 22B are mounted on top and bottom surfaces, with the electrode 22B grounded and a voltage V supplied to the electrode 22A. In such an arrangement, the piezoelectric element 31 undergoes a shear deflection.
Accordingly, by supplying a voltage V to the electrode 22A in a state in which the electrode 22B is grounded, the side on which electrode 22A of the shear-type piezoelectric element 31 is disposed deflects from an original state shown by dotted lines in FIG. 1B to a left side while the electrode 22B side deflects to a right side. As a result, by fixing the electrode 22B side in place, the electrode 22A side deflects in a direction indicated by the dotted arrow in FIG. 1A. Additionally, in this state, if instead the electrode 22A side were to be grounded and a voltage V supplied to the electrode 22B, the electrode 22A side would deflect in a direction indicated by the solid arrow in FIG. 1A.
A fuller description of this type of piezoelectric element used as a micro-actuator in a conventional head drive device will now be given, with reference to FIGS. 2A and 2B. A head drive device 58 comprises a fixing member 20 that acts as a base, a driving member 30 disposed atop the fixing member 20, and a movable member 40 positioned atop the drive member 30. The fixing member 20 corresponds to the main arm described above, the movable member 40 corresponds to the sub-arm described above, and the driving member 30 corresponds to the micro-actuator described above.
As shown in FIGS. 2A and 2B, an electrode 21 is disposed atop the fixing member 20, and is connected to a voltage generating part not shown in the diagram by a lead pattern 22. The driving member 30 comprises two piezoelectric elements 31 arranged in parallel. The directions of polarization of the two piezoelectric elements 31 that form the driving member 30 are as indicated by dotted-line arrows, that is, perpendicular to a direction of a thickness of the piezoelectric elements and exact opposites of each other. The movable member 40 stacked atop the driving member 30 is composed of an electrically conductive metal. The movable member 40 comprises a base portion 43 that rests directly on the two piezoelectric elements 31 and a movement expansion portion 44 (hereinafter extension 44) that projects from the base portion 43, with a first notch 41 cut into the base portion 43 so as to divide the base portion 43 into two. The first notch 41 lies in a direction parallel to the direction of polarization of the two piezoelectric elements 31 of the driving member 30. Further, a pair of second notches 42 are cut into a boundary portion between the base portion 43 of the movable member 40 and the extension 44 at both sides of the driving member 40, the second notches 42 being formed in a direction perpendicular to the direction in which the first notch 41 is formed. A hinge 45 is formed between a tip of the first notch 41 and tips of the second notches 42.
FIG. 2B shows the head drive device 58 and actuator 52 of FIG. 2A in an assembled state. The electrode 21 of the fixing member 20 is connected to a controller 18 via an amplifier 19, in such a way that the movable member 40 and the controller 18 are grounded. Accordingly, when a drive signal of a predetermined polarity is output from the controller 18, this signal is amplified by the amplifier 19 and a predetermined voltage is supplied across the thicknesses of the two piezoelectric elements 31, causing the movable member 40 to shift in the direction of the dotted arrow.
As a result, the movable member 40 (head suspension) shown in FIGS. 2A and 2B is moved slightly by driving the piezoelectric elements 31 (the micro-actuator) at the tip of the fixing member 20 (the main arm), so the head fixedly mounted at the tip of the head suspension can be precisely positioned, thus forming a head drive device.
However, in the above-described head drive device, when the micro-actuator is driven so as to position the head, the drive reactive force and the inertia created by the movement of the center of gravity of the head suspension generates a vibrational force that excites the carriage and causes the arm to vibrate. In that event, then no matter how high the resonance frequency of the micro-actuator, the flexural mode of the arm appears together with the driving of the micro-actuator. The cycle of that flexural mode is the main resonance frequency as determined by the servo band, resulting in an inability to precisely position the head.
Accordingly, it is necessary to avoid exciting the arm when driving the micro-actuator in order to be able to position the head precisely.
One solution to this problem has been proposed by Japanese Laid-Open Patent Application No. 9-161425, in which the head is supported by a low-rigidity spring and the center of gravity is identical to the center of rotation of the arm, such that a relatively small force suffices to drive the micro-actuator.
However, in such a head drive device, the primary resonance frequency is a relatively low several hundred Hz, such that antiresonance shows up in the transfer function of the voice coil motor-driven head displacement, making accurate control difficult.
Another, more basic solution to the problem of head vibration is to reduce the mass of the head drive device. However, restrictions imposed by the shape of the head suspension and so forth limit the amount by which the mass of the head drive device can be reduced.
Accordingly, it is an object of the present invention to provide an improved and useful magnetic head drive device in which the above-described disadvantage is eliminated.
The above-described object of the present invention is achieved by a head drive device for positioning a read and/or write head for reading and/or writing information to and from a disk coated with a recording medium, the head drive device comprising:
a carriage;
a main actuator for moving the carriage;
a plurality of heads for reading and/or writing information to and from the disk; and
a vibration control portion comprising a plurality of micro-actuators positioned between the carriage and the heads,
such that when the main actuator and a first micro-actuator are driven to enable precise positioning of a desired head with respect to a surface of the disk a second micro-actuator is driven so as to cancel vibrations generated at the carriage by the operation of the desired micro-actuator.
According to this aspect of the invention, eliminating the vibrations generated by the first micro-actuator improves the precision with which the head can be positioned with respect to the disk, providing a head drive device capable of the precise positioning required with the narrow track widths of high-density recording.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.